The invention relates to a heald shaft having shaft rods and end binders.
As rule, heald shafts comprise two spaced, mutually parallel held shaft rods which, at their ends, are connected to one another by end binders. In the position of rest, the end binders and the shaft rods form a rectangular frame. The shaft rods are provided with shaft staves which support healds. Each heald has at least one yarn-guiding eyelet through which a warp yarn passes.
During the weaving process, the heald shafts are, for shed-building, rapidly reciprocated vertically, whereby large dynamic loads are generated.
U.S. Pat. No. 4,022,252 describes a heald shaft having a rigid connection between the two vertically oriented end binders and the two horizontal shaft rods. During the upward and downward motions the shaft rods bend upward and downward. The shaft rods transmit such a bending through the rigid corner connection to the end binders, which, as a result, are bent in an S shape.
Since a bending of the end binders has been considered disadvantageous, attempts have been made to avoid such an occurrence. For this purpose, Japanese Patent No. 59-73382 discloses a jointed corner connection between end binder and shaft rod. The jointed corner connection is provided by a connecting joint situated inside the shaft rod. A projection extends from the end binder into the inner space thereof where it surrounds a bearing pin.
In such a basic configuration the bending of the shaft rod is not transmitted directly to the end binder. The latter has to take up only those bending moments which are generated by the introduction of forces from the shaft rod into the projection extending away from the end binder. At high dynamic loads this arrangement likewise results in a dynamic bending of, or loads on, the end binders.
Further, Japanese Patent No. 10-310948 discloses a heald shaft, whose end binders and shaft rods are connected to one another by connecting joints. The pivot axes of the connecting joints pass approximately centrally through the end binders. The connecting joints comprise spring elements which impose the 90° position on the connecting element and rapidly reset any deviation from such a 90° position.
The spring elements introduce forces into the end binders as soon as the shaft rod bends under dynamic loads.
The Japanese Patent No. 10-310948 further describes a direct drive of the heald shaft by driving couplers which are applied either to the end binders or to the lower shaft rod. In case the driving couplers are applied to the end binders, the force introduction into the end binders is effected by a linear motor or laterally projecting arms.
It is an object of the invention to improve a heald shaft regarding its dynamic design.